The prior art includes a variety of pneumatically powered tire changing apparatus. One such apparatus is shown in U.S. Pat. No. 3,212,552 issued to Foster which shows a single lever for translating the motion of the power source into movement of the upper and lower bead breaker shoes and rotation of the tired tool drive shaft. Such tire changing stands are most often used in service stations or garages or the like where there is a supply of compressed air. It is desirable to use the compressed air to drive the functional components of such tire changing stands because of the greater speed which is possible.
A substantial problem has developed with respect to the use of such pneumatically powered tire changing stands in conjunction with magnesium wheels. Such wheels have become quite popular because of their relative lightness and attractiveness when a chrome plating is applied thereto. Such magnesium wheels however are somewhat brittle and tend to crack easily. Personnel using the existing mechanisms ordinarily will not attempt to either remove or install a tire on such a magnesium wheel and in those cases where such work is done it is often done at the risk of the owner of the wheel. Cracks which do occur are not repairable and because such wheels often cost an excess of $50 each there is a significant problem in changing such tires.
Accordingly, it is a primary object of the invention to provide simple apparatus which may be readily manufactured, which will permit the use of the existing machine in conjunction with magnesium wheels.
More particular, a problem with the prior art apparatus has been a tire hold down member has been used having a tapered exterior surface which rests on the inside diameter of the magnesium wheel. Accordingly, there is line contact between the hold down member and the wheel resulting in high stress concentration during the mounting removal operation.